Method of firing a glass melting furnace with oxygen

ABSTRACT

A method for melting and refining glass, such as E glass, comprises feeding glass batch materials into a melting and refining tank for melting and refining the glass batch materials into glass and a forehearth, downstream of the tank, for further refining the glass and delivering the glass to fiberizing means. The melting and refining tank is heated with oxygen fired burners. The oxygen fired burners in the melting and refining tank are located in the sidewalls at the upstream end of the tank and extend for about one-third, one-half or two-thirds the length of the tank. In one embodiment, burners are also located in the upstream end wall. This arrangement of the oxygen fired burners at the upstream end of the melting and refining tank moves the melter hot spot upstream for better refining of the glass and enables the furnace to produce a higher output of glass than can be obtained in a conventional E glass furnace of the same size.

This application is a division of application Ser. No. 07/944,552, filedSep. 14, 1992, now abandoned.

FIELD OF THE INVENTION

This invention relates to an apparatus and method for producing glassfilaments and other glass products by melting and refining glass in afurnace that uses oxygen fired burners in the upstream end of themelting and refining tank.

BACKGROUND OF THE INVENTION

In the manufacture of glass, such as E glass fibers or filaments, by acontinuous melting process, glass batch material is delivered to afurnace at the upstream end of the melting and refining tank. The glassbatch material is melted and refined as it passes through the meltingand refining tank to a forehearth which is connected to the downstreamend of the melting and refining tank. The glass is withdrawn from themelting and refining tank into a conditioning section of the forehearthfrom which the glass passes to the working forehearth where the glass isdistributed to fiber forming equipment and withdrawn from the forehearththrough the fiber forming equipment to form the fibers or filaments.

In conventional E glass furnaces of the type shown in FIG. 1, the glassbatch materials are melted by directly opposed air/gas fired burnerswhich extend for substantially the entire length of the melting andrefining tank. The forehearth is also fired with directly opposedair/gas burners to further refine the glass and to regulate and maintainthe glass at the desired temperature for the fiber or filament formingprocess.

In a typical combustion process using an air/gas fired burner, naturalgas and air is usually combined in a set ratio of 10 parts air to 1 partnatural gas by volume. The main drawback to this method of combustion isthe nitrogen content of air which constitutes 78% of air by volume andcontributes nothing to the combustion process. Thus with air/gas firedburners, large volumes of air are required relative the volume ofnatural gas consumed. The relatively large volumes of combustion air andthe resulting large volumes of exhaust gases which must be processedusing air/gas fired burners require the use of costly, high volumecombustion air and exhaust gas systems.

For more efficient combustion, the air supplied to the air/gas firedburners should be preheated from ambient temperatures to temperatures ofabout 1200 degrees Fahrenheit. Since the volume of air to natural gasemployed by the burners is approximately 10 to 1, relatively largevolumes of air must be heated to these high temperatures and deliveredto the burners for use in the process. This requires the use of hightemperature metal recuperators to preheat the combustion air and hightemperature metal piping and insulation to deliver the hot air to theburners. These recuperators are expensive to construct and, with thehighly corrosive exhaust gases that pass through them, costly tomaintain.

In addition to greatly increasing the volume of gases to be preheatedand handled in the combustion system, the presence of nitrogen in theair detracts from the heating process by carrying part of the heat ofcombustion away from the process. Thus, part of the heat of combustiongoes to the nitrogen rather than to the glass melt for which it isintended and contributes nothing to the process. The presence ofnitrogen in the combustion process also leads to the formation ofnitrogen oxide emissions.

The low efficiencies of the air/gas fired burners require the use of alarge number of burners along substantially the entire length of themelting and refining tank in order to melt and refine the glass batchmaterials. The furnace illustrated in FIG. 1 uses a total of thirty-twoair/gas fired burners in the melting and refining tank.

BRIEF DESCRIPTION OF THE INVENTION

The melting and refining system of the present invention solves many ofthe problems associated with the air/gas fired E glass furnaces of theprior art. The use of commercially available oxygen-fuel or oxygen/gasfired burners located in the melting and refining tank adjacent theupstream end of the tank in accordance with the present invention canreduce the number of burners required in the melting and refining tankby as much as 75%. This result was not expected by those experienced inthe refining of glass in E glass unit melters and on the first furnaceinstallation more oxygen/gas fired burners were installed than wererequired. It was only after the furnace had been placed in operationthat it was determined that the burners located closest to theforehearth or downstream end of the melting and refining tank were notneeded. This reduction in the number of burners and related equipmentrequired to heat the furnace simplifies the control system for thefurnace while improving the process.

The air/gas fired burners use 10 parts air to 1 part natural gas byvolume. The oxygen/gas fired burners use 2 parts oxygen to 1 partnatural gas by volume. By greatly reducing the volumes of the productsof combustion, there is no longer a need for the costly combustion airsystems used with the air/gas fired burners in the E glass furnaces ofthe prior art. In addition, costly recuperators along with theassociated piping, control and monitoring systems can be eliminated andthe maintenance time and expense associated with the use of thesesystems in a highly corrosive atmosphere can be eliminated too.

The oxygen/gas fired burners have a more luminous flame than the flameof the air/gas fired burners. This results in better heat transfer tothe glass batch materials and a reduction in the natural gas usage forthe furnace of about one-third due to the better heat transfer and theelimination of the need to heat up the large volumes of nitrogen foundin the air used in the air/gas fired burners.

In the present invention, approximately one third the length, preferablyone half the length and up to two thirds the length, of the sidewalls ofthe melting and refining tank, adjacent the downstream end of said tank,have no burner means. With the oxygen/gas fired burners located adjacentthe upstream end of the melting and refining tank where the glass batchmaterials are introduced into the furnace and with the better heattransfer from the flames of the oxygen/gas fired burners to the glassbatch materials, the glass batch materials melt faster moving themelting and refining tank hot spot closer to the upstream end of themelting and refining tank. This has the effect of increasing the volumeof the bath within the tank that is available for refining the glass andincreases the capacity of the furnace over an air/gas fired furnace ofthe same size.

By reducing the products of combustion from 11 parts to 3 parts, andeliminating the nitrogen present in air/gas combustion, emissions aregreatly reduced with less particulate carryover going out of the meltingand refining tank. Corrosive volatiles which later condense and causemaintenance problems are also reduced.

With less exhaust emissions being produced by the furnace, the back wallexhaust port of the melting and refining tank can be reduced in size.This permits the movement of the doghouses from the sidewalls of themelting and refining tank to the upstream wall or back wall of themelting and refining tank. This too has the effect of increasing themelting and refining portion of the melting and refining tank andcontributes to increasing the capacity of the furnace.

As discussed in the article, MANVILLE PLANT GETS A BOOST FROM OXYGEN-GASFIRING, pp.10-14, GLASS INDUSTRY, January 1992, oxygen-gas firing hasbeen used in glass furnaces for lower temperature melting of glass toproduce insulation fiber. Oxygen/gas firing has also been used inregenerative melters for making glass bottles as discussed in thearticle, HOW 100% OXYGEN FIRING IMPACTS REGENERATIVE MELTERS, pp. 12-14,17-20, 25 and 26, GLASS INDUSTRY, March 1992.

However, to Applicants' knowledge, the subject invention is the firsttime oxygen/gas firing has been used in an E glass furnace with itsrelatively high temperature operating conditions. High temperatureglasses, such as E glass, are glasses containing less than 3% alkalioxide and usually less than 1.5 percent alkali oxide. For proper meltingand refining, these glasses require furnace temperatures in excess of2750 degrees Fahrenheit and usually above 2850 degrees Fahrenheit. Sincethese temperatures are very near the maximum safe operating temperaturesfor the furnace lining refractories, there was a concern that oxygen/gasfired burners, with hotter flame temperatures than the air/gas firedburners, would overheat the furnace lining in places damaging therefractories. After the furnace was placed in operation, it wasdetermined that the overheating did not occur.

In addition to the above, the unique placement of the oxygen/gas firedburners at the upstream end of the furnace was found to enhance themelting and refining capabilities of the furnace. This unique placementof the oxygen/gas fired burners is not disclosed in the above mentionedarticles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan schematic view of a typical air/gas fired melting andrefining tank of the prior art.

FIG. 2 is a plan schematic view of a first embodiment of the oxygen/gasfired melting and refining tank of the present invention.

FIG. 3 is a plan schematic view of a second embodiment of the oxygen/gasfired melting and refining tank the present invention.

FIG. 4 is a plan schematic view of a forehearth.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a typical prior art air/gas fired melting andrefining tank 12 which is used in the manufacture of E glass fibers orcontinuous glass filaments. The melting and refining tank 12 can vary insize but is typically 40 to 50 feet long by about 20 feet wide and ismade of refractory materials to withstand the high temperatures requiredto melt and refine E glass batch materials into E glass. The downstreamend of the melting and refining tank 12 is directly connected to aforehearth, such as forehearth 14 of FIG. 4, and the glass flows fromthe melting and refining tank 12 into the forehearth where the glass isfurther refined and distributed to the fiberizers of the fiber orcontinuous filament forming process.

As shown in FIG. 1, the E glass batch materials are fed into the meltingand refining tank 12 through doghouses 16 and 18 which are located oneither side of the melting and refining tank adjacent the upstream endof the melting and refining tank 12. After the glass batch materials areintroduced into the melting and refining tank 12, the glass batchmaterials are melted and refined as they pass through the melting andrefining tank to the forehearth 14. The glass batch materials areheated, melted and refined by air/gas burners 20 which extend forsubstantially the entire length of the melting and refining tank fromthe doghouses 16 and 18 to the downstream end of the melting andrefining tank where the glass flows into the forehearth 14. In thefurnace shown, each sidewall of the melting and refining tank 12 isprovided with 16 air/gas fired burners 20 spaced from each other ontwenty-one inch centers and directly opposite the burners 20 on theopposing sidewall. With the large number of air/gas fired burners 20required to melt and refine the glass batch materials, costly combustionair preheating and exhaust gas recuperator systems are required in amanufacturing process using air/gas fired burners. A large exhaust port22 and exhaust stack 23 is provided at the upstream end of the meltingand refining tank 12 to accommodate the large volumes of exhaust gasesproduced by the process.

FIG. 2 illustrates a first embodiment of the present invention with an Eglass melting and refining tank 26 that has the same dimensions as themelting and refining tank 12 of the prior art. The melting and refiningtank 26 uses conventional oxygen/gas fired burners 28 such as MaxCor,OXY-THERM burners or Combustion Tec, Inc., CLEANFIRE burners. As shown,there are three oxygen/gas fired burners 28 in each sidewall of themelting and refining tank downstream of the doghouses 30 and 32 and twooxygen-fuel or oxygen/gas fired burners 34 in the back wall or upstreamwall of the melting and refining tank 26 on either side of the exhaustport 36 which leads to exhaust stack 37. The oxygen/gas fired burners 28are located fourteen inches plus or minus four inches above the surfaceof the glass melt and are spaced apart a distance about twice that ofthe air/gas fired burners 20 of the prior art E glass melting andrefining tank with the oxygen/gas fired burners being spaced aboutforty-two inches apart.

The oxygen/gas fired burners 28 have a much higher BTU output per burnerthan the air/gas fired burners 20 and in accordance with the presentinvention the burners on one sidewall are offset with respect to theburners 28 in the other sidewall to effect a better heat distribution inthe upstream portion of the melting and refining tank 26. Thisarrangement of the oxygen/gas fired burners in the sidewalls plus theplacement of the two burners 34 in the upstream end wall moves the hotspot closer to the upstream end of the melting and refining tank. Thishas the effect of increasing the melting and refining area of thefurnace without increasing the size of the melting and refining tank 26.Thus, the capacity of the melting and refining tank is increased.

By reducing the number of burners in the melting and refining tank 26 byas much as 75%, the burner control system is greatly simplified. Inaddition, the reduction in the number of burners and the use of oxygengreatly reduces the volumes of gases used in the process and eliminatesthe need to preheat the combustion air as was required in the prior artprocess. Thus, the present invention eliminates the need for combustionair preheating systems, recuperators and the associated piping, controland monitoring systems while increasing the capacity of the melting andrefining tank 26. As in the prior art E glass furnace, the glass flowsfrom the melting and refining tank 26 into the forehearth 14 where theglass is further refined and distributed to the fiberizing stations.

FIG. 3 illustrates a second embodiment of the present invention with anE glass melting and refining tank 38 which has the same dimensions asthe melting and refining tank 12 of the prior art. In this embodimentall eight of the oxygen/gas fired burners 40 are positioned in thesidewalls of the melting and refining tank adjacent the upstream end ofthe melting and refining tank 38. The oxygen/gas fired burners 40 in onesidewall are offset from the burners in the opposite sidewall and spacedfrom each other in the same manner as the burners 28 of the firstembodiment of the present invention. The burners are conventionaloxygen/gas fired burners, such as, MaxCor, OXY-THERM burners orCombustion Tec, Inc., CLEANFIRE burners.

As shown in FIG. 3, the doghouses 42 and 44 are both located in theupstream wall or back wall of the melting and refining tank 38. Thisallows the burners in the sidewalls to be located adjacent the back orupstream wall of the melting and refining tank 38.

Another method of introducing the E glass batch materials into themelting and refining tank 38 is through the use of several batchchargers located in the back or upstream wall of the tank. While the useof several batch chargers in the upstream wall of regenerative furnacesis known, batch chargers have not been used on unit melters because ofthe large exhaust gas chamber and recuperator stack support normallylocated adjacent the exterior of the upstream wall of air/gas fired unitmelters. The use of batch chargers eliminates the use of the doghousesand the exhaust gases are removed from the tank 38 and directed to theexhaust stack 46 through one or more openings in the back wall above thebatch chargers such as through the exhaust port 48. As with the use ofthe doghouses 42 and 44, the use of the batch chargers allows theburners to be located adjacent the back or upstream wall of the tank 38.

As with the first embodiment illustrated in FIG. 1, this arrangement ofthe oxygen/gas fired burners 40 and the doghouses 42 and 44 moves thehot spot of the melting and refining tank upstream and increases thecapacity of the melting and refining tank. The other advantagesdiscussed above are also realized.

While, for the purposes of illustration, the process has been describedusing oxygen/natural gas fired burners, it is to be understood thatpropane or oil fired burners can be substituted for the natural gasfired burners when these fuels are desired.

The present invention has proved to be very beneficial in the productionof glass filaments where highly refined homogeneous glass is required toproduce a good product. However, it is contemplated that this processcan be used to produce other glass products too.

What is claimed is:
 1. In a method of melting and refining glass in afurnace having a melting and refining tank with an upstream end, twosidewalls having oxygen-fuel fired burners therein, and a downstreamend, comprising:feeding batch into the tank adjacent the upstream endand melting said batch to form molten glass, subjecting said batch andmolten glass to heat from flames overhead generated by said burners, andremoving molten, refined glass at the downstream end of said tank, theimprovement comprising: feeding oxygen and fuel to all of said burners,said burners being spaced apart in a portion of each sidewall that isadjacent the upstream end, no burners being in a portion of each of saidsidewalls adjacent said downstream end of said tank, the portion of eachof said sidewalls having no burners having a length of at leastapproximately one third the length of each sidewall.
 2. The method ofclaim 1 wherein the batch is an E glass batch and wherein said refinedglass is suitable for forming into glass fibers.
 3. The method of claim1 wherein said burners are spaced apart in a portion of each sidewallthat is adjacent the upstream end of said tank and no burners are in aportion of said sidewall that is approximately one half the length ofeach sidewall that is adjacent the downstream end of said tank.
 4. Themethod of claim 3 wherein said fuel is a gas.
 5. The method of claim 3wherein said furnace also has an upstream end wall at the upstream endof said tank and some oxygen-fuel burners are also located in saidupstream end wall.
 6. The method of claim 1 wherein said fuel is a gas.7. The method of claim 1 wherein said furnace also has an upstream endwall at the upstream end of said tank and some oxygen-fuel burners arealso located in said upstream end wall.
 8. The method of claim 1 whereinsaid burners are spaced apart in a portion of each sidewall that isadjacent the upstream end of said tank and no burners are in a portionof said sidewall that is approximately two thirds the length of eachsidewall that is adjacent the downstream end of said tank.
 9. The methodof claim 8 wherein said fuel is a gas.
 10. The method of claim 8 whereinsaid furnace also has an upstream end wall at the upstream end of saidtank and some oxygen-fuel burners are also located in said upstream endwall.
 11. The method of claim 1 wherein the oxygen and fuel are fed toall of said burners in a ratio of about 2 parts oxygen to about 1 partfuel.
 12. The method of claim 11 wherein said batch is an E-glass batch.